+1@pmm. When the (10dB) attenuator is used between the preamp and the power amp, quote (in Rothwell) "... not only is system gain reduced by 10dB but also the signal to noise ratio is improved by 10dB. This pushes the noise floor down enough to create an inky black silent background from which the music can emerge with better resolved fine detail and transparency. This applies to even very high-end and very expensive pre/power amps." end quote.
Harrison Lab carries -12dB rca inline attenuator too and has good feedback but no xlr. Also, I have used the variable attenuator a bit more expensive though.